media player sound/video dosn't match

[yimmortal]

ok when i play a video in windows media player it plays fine until i switch to full screen.. when i do that then the sound and video are out of sync.. any ideas on how to improve this

vista ultimate
4gb ram only shows that i have 3326????
nvidia GeGorce 7300LE video card
intel core2 6400 2.13ghz